Reduced pressure treatment system

ABSTRACT

A wound treatment apparatus is provided for treating tissue damage, which comprises a fluid impermeable wound cover sealed over a site for purposes of applying a reduced pressure to the site. The apparatus also includes a cover with protrusions on its surface for purposes of monitoring pressure at the site. An absorbable matrix may be placed in the site of a wound to encourage tissue growth into the matrix. Temperature of the site may be monitored using a layer of temperature sensitive material and temperature sensors connected to an alarm and recording device. A vacuum pump supplies suction within the wound cover over the treatment site. A portable version of the wound treatment apparatus is also provided. Finally, a method for treating wounds using reduced pressure is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/652,100, filed on Aug. 28, 2003, issued as U.S. Pat. No.7,846,141, and claims the benefit of U.S. Provisional Patent ApplicationNo. 60/407,783, filed on Sep. 3, 2002, and U.S. Provisional PatentApplication No. 60/430,827, filed on Dec. 4, 2002, the entirety of allthree of which are hereby incorporated by reference and made a part ofthe present disclosure as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for treatinga wound by applying reduced pressure to the wound. In this context, theterm “wound” is to be interpreted broadly, to include any body part of apatient that may be treated using reduced pressure.

2. Description of the Related Art

The treatment of open or chronic wounds that are too large tospontaneously close or otherwise fail to heal has long been atroublesome area of medical practice. Closure of an open wound requiresinward migration of surrounding epithelial and subcutaneous tissue. Somewounds, however, are sufficiently large or infected that they are unableto heal spontaneously. In such instances, a zone of stasis in whichlocalized edema restricts the flow of blood to the epithelial andsubcutaneous tissue forms near the surface of the wound. Withoutsufficient blood flow, the wound is unable to successfully fightbacterial infection and is accordingly unable to close spontaneously.

An initial stage of wound healing is characterized by the formation ofgranulation tissue which is a matrix of collagen, fibronectin, andhyaluronic acid carrying macrophages, fibroblasts, and neovasculaturethat forms the basis for subsequent epithelialization of the wound.Infection and poor vascularization hinder the formation of granulationtissue within wounded tissue, thereby inhibiting wound healing. Ittherefore becomes desirable to provide a technique for increasing bloodcirculation within wounded tissue to promote spontaneous healing and toreduce infection.

Another problem encountered during the treatment of wounds is theselection of an appropriate technique for wound closure during thehealing process. Sutures are often used to apply force to adjacentviable tissue in order to induce the edges of a wound to migratetogether and heal. However, sutures apply a closure force to only a verysmall percentage of the area surrounding a wound. When there isscarring, edema, or insufficient tissue, the tension produced by thesutures can become great causing excessive pressure to be exerted by thesutures upon the tissue adjacent to each suture. As a result, theadjacent tissue often becomes ischemic thereby rendering suturing oflarge wounds counterproductive. If the quantity or size of the suturesis increased to reduce the tension required of any single suture, thequantity of foreign material within the wound is concomitantly increasedand the wound is more apt to become infected. Additionally, the size ortype of a particular wound may prevent the use of sutures to promotewound closure. It therefore becomes desirable to provide an apparatusand method for closing a large wound that distributes a closure forceevenly about the periphery of the wound.

Wounds resulting from ischemia, or lack of blood flow, are also oftendifficult to heal since decreased blood flow to a wound may inhibitnormal immune reaction to fight infection. Patients that are bedriddenor otherwise non-ambulatory are susceptible to such ischemic wounds asdecubitus ulcers or pressure sores. Decubitus ulcers form as a result ofconstant compression of the skin surface and underlying tissue thusrestricting circulation. Since the patient is often unable to feel thewound or to move sufficiently to relieve the pressure, such wounds canbecome self-perpetuating. Although it is common to treat such woundswith flaps, the conditions that initially caused the wound may also workagainst successful flap attachment. Wheelchair-bound paraplegics, forexample, must still remain seated after treatment of pelvic pressuresores. It therefore becomes desirable to provide a treatment procedurefor ischemic wounds that can be conducted in situ upon an immobile orpartially mobile patient.

Other types of wounds in which ischemia leads to progressivedeterioration include partial thickness burns. A partial thickness burnis a burn in which the cell death due to thermal trauma does not extendbelow the deepest epidermal structures such as hair follicles, sweatglands, or sebaceous glands. The progression of partial thickness burnsto deeper burns is a major problem in burn therapy. The ability tocontrol or diminish the depth of burns greatly enhances the prognosisfor burn patients and decreases morbidity resulting from burns. Partialthickness burns are formed of a zone of coagulation, which encompassestissue killed by thermal injury, and a zone of stasis. The zone ofstasis is a layer of tissue immediately beneath the zone of coagulation.Cells within the zone of stasis are viable, but the blood flow is staticbecause of collapse of vascular structures due to localized edema.Unless blood flow is re-established within the zone of stasis soon afterinjury, the tissue within the zone of stasis also dies. The death oftissue within the zone of stasis is caused by lack of oxygen andnutrients, reperfusion injury (re-establishment of blood flow afterprolonged ischemia), and decreased migration of white blood cells to thezone resulting in bacterial proliferation. Again, it becomes desirableto provide a technique for treating burn wounds by enhancing bloodcirculation to the wounded tissue to inhibit burn penetration.

There exist various apparatus utilizing reduced pressure for treatmentof these types of wounds. See, for example, U.S. Pat. No. 5,636,643. Theapparatus existing in the art is generally comprised of a fluidimpermeable cover that covers the wound, which is directly or indirectlyconnected to a source of suction so that an area of reduced pressure iscreated beneath the cover in the area of the wound. Some type of packingmaterial, such as gauze, is also often placed in the area of the woundbeneath the cover to prevent overgrowth of the wound. Apparatus existingin the relevant art, however, suffer from several disadvantages.

One such disadvantage is the necessity to change the packing materialplaced in the wound during the period of treatment. This requirement isexpensive because multiple dressings are necessary and medical staffmust expend time to change the dressings. In addition, there is anincreased risk of infection and intrusion of other harmful foreignmaterial into the wound area. It is therefore desirable to have areduced pressure wound treatment system having a dressing that does notneed to be changed, or needs to be changed fewer times, during theperiod of treatment.

In addition, the existing apparatus do not have adequate means tomonitor the pressure in the area of the wound beneath the cover. If thecover is not adequately sealed to the tissue surrounding the wound,reduced pressure cannot be maintained beneath the cover so that thebenefits of the treatment are lost or diminished. In addition, pressureleaks through the seal cause the source of suction to operate morefrequently, which consumes more energy and causes the suction equipmentto wear faster than it would otherwise, reducing its useful life.Further, the flow of air into the wound area as a result of such leakscan result in increased risk of infection and intrusion of other harmfulforeign material into the wound area. It is therefore desirable to havea relatively inexpensive means of monitoring the pressure level beneaththe cover at the site of the wound.

In addition, the existing apparatus do not have a means to determine theamount of blood flow to the tissue at the site of the wound. Asdiscussed above, adequate blood circulation in the area of the wound isessential for the healing process to proceed as desired. Areas of tissuehaving an increased level of blood circulation generally have a highertemperature than areas that have a comparatively lower level of bloodcirculation. It is therefore desirable to have a means of monitoring therelative temperature within the area of the wound.

Finally, it is sometimes necessary to transport patients in need ofreduced pressure wound care. It is also sometimes necessary to providereduced pressure treatment in the field. It is therefore also desirableto have a wound treatment apparatus that is portable and self-contained,which can accompany the patient during such transport or be used toprovide reduced pressure treatment in the field.

SUMMARY

The present invention is directed to a reduced pressure wound treatmentapparatus and method that satisfy the needs described above. Asdescribed in greater detail below, it has many advantages over existingapparatus when used for its intended purpose, as well as novel featuresthat result in a new reduced pressure wound treatment apparatus andmethod that are not anticipated, rendered obvious, suggested, or evenimplied by any of the prior art apparatuses, either alone or in anycombination thereof.

In accordance with the present invention a wound treatment apparatus isprovided for treating a wound by applying reduced pressure (i.e.pressure that is below ambient atmospheric pressure) to the wound in acontrolled manner for a selected time period in a manner that overcomesthe disadvantages of currently existing apparatus. The application ofreduced pressure to a wound provides such benefits as faster healing,increased formation of granulation tissue, closure of chronic openwounds, reduction of bacterial density within wounds, inhibition of burnpenetration, and enhancement of flap and graft attachment. Wounds thathave exhibited positive response to treatment by the application ofnegative pressure include infected open wounds, decubitus ulcers,dehisced incisions, partial thickness burns, and various lesions towhich flaps or grafts have been attached.

The wound treatment apparatus in accordance with the present inventionincludes a reduced pressure application appliance that is applied to atreatment site at which there is a wound and normal tissue surroundingthe wound. The reduced pressure application appliance includes a fluidimpermeable wound cover for covering and enclosing the wound. In aparticular embodiment of the present invention, the wound cover alsoincludes means for visually monitoring the pressure in the area of thesite of the wound beneath the wound cover. These means include aplurality of protrusions on the surface of the cover that are recessedwhen a predetermined pressure is present beneath the cover, but areincreasingly displaced above the remaining surface of the cover as thepressure beneath the cover increases above a predetermined pressure. Ina similar manner, the cover may contain areas that are displaced asprotrusions away from the remaining surface of the cover toward thewound when reduced pressure is applied beneath the cover, and thedisplacement of the protrusions decreases as the pressure beneath thecover increases. The protrusions may also be a different color (or adifferent shade of the same color) from that on the remaining surface ofthe cover. In addition, the protrusions may produce a noise as they aredisplaced away from the remaining surface of the cover, providing anaudible indication that the pressure beneath the cover is increasing.

The appliance also includes sealing means for sealing the wound cover tothe surrounding tissue of the wound in order to maintain reducedpressure in the vicinity of the wound during wound treatment. When thewound cover is sealed in position over the wound site, a generallyfluid-tight or gas-tight sealed enclosure is formed over the wound site.The sealing means may be in the form of an adhesive applied to theunderside of the wound cover for sealing the wound cover around theperiphery of the wound. The sealing means may also include a separatesealing member such as an adhesive strip or a sealing ring in the formof a tubular pad or inflatable cuff secured to the wound cover forpositioning around the periphery of the wound. In selected embodiments,the reduced pressure within the sealed enclosure under the wound covermay serve to seal the wound cover in position at the wound site. Thereduced pressure appliance also includes a suction port for supplyingreduced pressure within the sealed volume enclosed beneath the woundcover. The suction port may be in the form of a nipple on the woundcover. Alternatively, the suction port may be in the form of a tubeattached to the wound cover or provided as a feedthrough beneath thewound cover.

The appliance may also include an absorbable matrix for placement in thewound in order to encourage tissue in the area of the wound to grow intothe matrix during treatment. The absorbable matrix is constructed of anabsorbable material that is absorbed into the epithelial andsubcutaneous tissue in the wound as the wound heals. The matrix may varyin thickness and rigidity, and it may be desirable to use a spongyabsorbable material for the patient's comfort if the patient must lieupon the appliance during treatment. The matrix may also be perforatedand constructed in a sponge-type or foam-type structure to enhance gasflow and to reduce the weight of the matrix. Because of the absorbablenature of the absorbable matrix, the matrix should require less frequentchanging than other dressing types during the treatment process. Inother circumstances, the matrix may not need to be changed at all duringthe treatment process.

A vacuum system is connected with the reduced pressure appliance inorder to provide suction or reduced pressure to the appliance. For thispurpose, the vacuum system includes a suction pump or suction device forconnection with the suction port of the appliance for producing thereduced pressure over the wound site. The vacuum system may include asection of hose or tube, such as a vacuum hose, that interconnects thesuction device with the suction port of the appliance to provide thereduced pressure at the wound site. A fluid collection system may beprovided intermediate the vacuum hose of the suction device and thesuction port of the appliance to trap any exudate that may be aspiratedfrom the wound by the negative pressure appliance. A stop mechanism mayalso be provided for the vacuum system to halt production of the reducedpressure at the wound site in the event that an excessive quantity ofexudate has been collected. The apparatus may also include a controldevice for controlling the pump.

In a particular embodiment of the invention, the wound cover for thereduced pressure appliance may be in the form of a gas impermeablecovering sheet of flexible polymer material, such as polyethylene,having an adhesive backing that provides the seal for securing the sheetover the wound site to provide a gas-tight or fluid-tight sealedenclosure over the wound site. The vacuum system of the wound treatmentapparatus may include a suction pump having a vacuum hose that isconnected with a suction tube serving as a suction port for theappliance. The suction tube for the appliance runs beneath the coversheet that is sealed in position over the wound site and into thefluid-tight enclosure provided under the cover sheet. An adhesivebacking on the cover sheet is used to provide a fluid-tight seal aroundthe feedthrough for the suction tube at the wound site. Within theenclosure, the suction tube is connected with the absorbable matrix forplacement in the wound. The absorbable matrix functions to moreuniformly apply reduced pressure or suction over the wound site whileholding the cover sheet substantially out of the wound during theapplication of reduced pressure at the enclosed wound site.

In another particular version of the invention, the wound treatmentapparatus also includes means to monitor the temperature of the tissuein the area of the wound. In a particular embodiment of this version ofthe invention, a temperature sensitive layer composed of a temperaturesensitive material is placed adjacent to the lower surface of the woundcover. The temperature sensitive layer changes color, or changes fromone shade of a color to another shade of the same color, as thetemperature of the material changes. In this embodiment of theinvention, the wound cover is composed of a transparent orsemi-transparent material allowing the temperature sensitive material tobe observed from above the wound cover. Alternatively, the wound coveris composed of a temperature sensitive material that changes color, orchanges from one shade of a color to another shade of the same color, asthe temperature of the material changes. In another embodiment of thisversion of the invention, one or more temperature measuring devices areplaced in the area of the wound. The temperature measuring devices arepreferably placed adjacent to the wound tissue, but may also be placedin other locations under or above the wound cover, to monitor thetemperature of said tissue. Temperature measuring devices located underthe wound cover have leads that feedthrough beneath the wound cover. Theleads are connected to an alarm system that produces one or more alarmsignals when the temperature measured by one or more of the temperaturemeasuring devices exceeds or is lower than a predetermined value. Inanother embodiment of this version of the invention, the temperaturemeasuring devices are also connected through their respective leads andthe alarm system to a temperature display or recording device thatproduces a display or record of the temperature in the area of thewound.

In another particular version of the invention, the wound treatmentapparatus is portable and self-contained. In this version of theinvention, a miniature vacuum source is used to provide suction to thereduced pressure appliance. Similarly, the fluid collection system is ofthe minimum size desired to collect and maintain the amount of exudateexpected to be aspirated from the wound during the time of anticipateduse of the portable wound treatment apparatus. A filter may also beplaced in the connection between the vacuum source and the fluidcollection system to avoid contamination of the source by the fluidaspirated from the wound. As a result, reduced pressure treatment of awound can continue even if it becomes necessary to transport the patientbecause the apparatus can accompany a patient during the transport. Theportable apparatus is not, however, limited to this use alone. It can beused in any application where a portable treatment apparatus isadvantageous, such as treatment of wounds in the field.

There has thus been outlined, rather broadly, the more primary featuresof the present invention. There are additional features that are alsoincluded in the various embodiments of the invention that are describedhereinafter and that form the subject matter of the claims appendedhereto. In this respect, it is to be understood that the invention isnot limited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the following drawings. This invention may be embodied inthe form illustrated in the accompanying drawings, but the drawings areillustrative only and changes may be made in the specific constructionillustrated and described within the scope of the appended claims. Theinvention is capable of other embodiments and of being practiced andcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein are for the purpose of thedescription and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the present invention, will be betterunderstood when read in conjunction with the appended drawings, inwhich:

FIG. 1 is a schematic elevational view of a wound treatment apparatus inaccordance with a particular embodiment of the present invention inwhich a reduced pressure appliance, shown in partial section, includes aflexible, fluid impermeable wound cover sealed over the wound and anabsorbable matrix positioned in the wound, and in which a vacuum systemprovides reduced pressure within the wound cover of the appliance;

FIG. 2 a is a schematic sectional elevational view of the reducedpressure appliance of FIG. 1, illustrating an absorbable matrix havingthree layers of absorbable material, such layers being of differentabsorbable materials;

FIG. 2 b is a schematic sectional elevational view of the reducedpressure appliance of FIG. 1, illustrating an absorbable matrix havinggenerally concentric layers of absorbable material, such layers being ofdifferent absorbable materials;

FIG. 3 is a schematic sectional elevational view of a reduced pressureappliance in accordance with another embodiment of the presentinvention, shown in partial section, in which the reduced pressureappliance includes a rigid, fluid impermeable, cone-shaped wound coveroverlying the wound site;

FIG. 4 a is a schematic elevational view of a wound treatment apparatusin accordance with a particular embodiment of the present invention inwhich a reduced pressure appliance, shown in partial section, includes aflexible, fluid impermeable wound cover sealed over the wound and anabsorbable matrix positioned in the wound, and in which a vacuum systemprovides reduced pressure within the wound cover of the appliance;

FIG. 4 b is a sectional elevational detailed view of the shutoffmechanism portion of the collection system of FIG. 4 a;

FIG. 5 a is a schematic sectional elevational view of a reduced pressureappliance in accordance with another embodiment of the presentinvention, shown in partial section, in which the reduced pressureappliance includes a flexible, fluid impermeable wound cover sealed overthe wound, said cover having embedded within it protrusions that aredisplaced above the remaining surface of the cover;

FIG. 5 b is a detailed perspective view of a protrusion from the reducedpressure appliance of FIG. 5 a, in the fully displaced configuration;

FIG. 5 c is a schematic sectional elevational view of the reducedpressure appliance of FIG. 5 a, illustrating the cover having theprotrusions in the depressed configuration when sufficient vacuum ispresent beneath the cover;

FIG. 5 d is a detailed perspective view of a protrusion from the reducedpressure appliance of FIG. 5 a, in the fully depressed configuration;

FIG. 5 e is a schematic sectional elevational view of the reducedpressure appliance of FIG. 5 a, illustrating alternative protrusionshaving a bellows-type of configuration;

FIG. 5 f is a perspective view of the reduced pressure appliance of FIG.5 a, illustrating a pattern of protrusions on the wound cover;

FIG. 6 is a schematic sectional elevational view of a reduced pressureappliance in accordance with another embodiment of the presentinvention, shown in partial section, in which the reduced pressureappliance includes a packing material or an absorbable matrix positionedin the wound, and a flexible, fluid impermeable wound cover sealed overthe wound, and a layer of temperature sensitive material located betweenthe cover and the wound;

FIG. 7 is a schematic sectional elevational view of a reduced pressureappliance in accordance with another embodiment of the presentinvention, shown in partial section, in which the reduced pressureappliance includes a packing material positioned in the wound, and aflexible, fluid impermeable wound cover sealed over the wound, and aplurality of temperature sensors located at and surrounding the site ofthe wound, and in which an alarm system and a temperature display andrecording device are connected to the temperature sensors;

FIG. 8 a is a perspective view of a wound treatment apparatus inaccordance with another embodiment of the present invention, shown fromabove, in which a reduced pressure appliance, a vacuum source, a filter,and a fluid collection system are connected together as a compact andportable apparatus; and

FIG. 8 b is a sectional elevational detailed view of the shutoffmechanism portion of the collection system of FIG. 8 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the present invention, a wound treatment apparatus isprovided for treating a wound by application of reduced pressure (i.e.,below atmospheric pressure) so that suction may be applied to a woundsite 25 in a controlled manner for a selected period of time. FIG. 1schematically shows one version of the wound treatment apparatus,generally designated 20, which includes a reduced pressure appliance,generally designated 30, for enclosing a wound site 25 to provide afluid-tight or gas-tight enclosure over the wound site 25 to effecttreatment of a wound 25 with reduced or negative pressure. For thepurpose of creating suction within the appliance 30, the appliance 30 isconnected with a vacuum system, generally designated 50, to provide asource of suction or reduced pressure for the sealed appliance 30 at thewound site 25. Intermediate the appliance 30 and the vacuum system 50 isa fluid collection system, generally designated 70, for intercepting andretaining exudate that is aspirated from the wound site 25.

FIG. 1 also illustrates one embodiment of the reduced pressure appliance30, which includes an absorbable matrix 32 that is placed within thewound 25, a fluid impermeable wound cover 40, and a suction port in theform of hollow tubing 45 that connects the appliance 30 to the vacuumsystem 50 (through the collection system 70) to provide reduced pressurein the area beneath the cover 40 in the area of the wound 25. FIG. 1also illustrates one embodiment of an absorbable matrix 32, which isplaced within the wound 25.

The absorbable matrix 32 is placed over substantially the expanse of thewound 25 to encourage growth of tissue in the area of the wound 25 intothe matrix 32 as the wound heals. The size and configuration of theabsorbable matrix 32 can be adjusted to fit the individual wound 25. Itcan be formed from a variety of absorbable materials, preferably amaterial that is also porous. The matrix 32 should be constructed in amanner so that it is sufficiently porous to allow oxygen to reach thewound 25. The absorbable matrix 32 is preferably constructed of anon-toxic material that is absorbable by the epithelial and subcutaneoustissue within the area of the wound 25, such as collogens derived fromhealthy mammals, absorbable synthetic polymers, or other materialssimilar to those used for absorbable dressings. An example is adehydrating material derived from seaweed for treatment of exudatingwounds. The matrix 32 may vary in thickness and rigidity, although itmay be desirable to use a spongy or layered, non-woven absorbablematerial for the patient's comfort if the patient must lie upon theappliance 30 during treatment. The matrix 32 may also be perforated andconstructed in a foam-type, sponge-type, or non-woven layered structureto enhance gas flow and to reduce the weight of the appliance 30. Asshown in FIG. 1, the matrix 32 is cut to an appropriate shape and sizeto fit within the wound 25. Alternatively, the matrix 32 may besufficiently large to overlap the surrounding skin 24. Further, thematrix 32 may be of uniform thickness over its entire area, as is thecase where monitoring the temperature of tissue in the area of the woundis desired as a part of the treatment process.

In another embodiment of the invention, the absorbable matrix 32 has thesame features as described above and as illustrated in FIG. 1, but mayalso be constructed of more than one absorbable material, such materialhaving different rates of absorption into body tissue. By preselectingthe materials of the matrix 32, and placing them in areas of the wound25 in which different rates of absorption are desired, it may bepossible to enhance wound healing. An example of this embodiment of theabsorbable matrix 32 is illustrated in FIG. 2 a, where the matrix 32 iscomposed of three layers, each layer being composed of an absorbablematerial different from the material in the adjacent layer. Thus, in amatrix 32 of three layers having the lowest layer 33 being constructedof an absorbable material, and the middle layer 34 of the matrix 32being constructed of a material having a lower rate of absorption thanthe lowest layer 33, and the layer of the matrix 32 closest to the cover40 (i.e., the highest layer 35) being constructed of a material having arate of absorption lower than the other two layers, the area of thewound 25 adjacent to the lowest layer 26 would be allowed to close at afaster rate than the area of the wound 25 adjacent to the middle layer27, and the area of the wound 25 adjacent to the highest layer 28 wouldbe allowed to close at a faster rate than the area of the wound 25adjacent to the middle layer 27 and the lowest layer 26. This embodimentof the invention is not limited to three layers or this gradation ofabsorption rates. Any combination of number of layers and absorbentmaterials desirable for wound treatment is possible and may bepreferred. For example, the matrix 32 may have a highest layer 35 ofabsorbent material having a rate of absorption higher than the rate ofabsorption of the middle layer 34, which middle layer 34 has a higherrate of absorption than the rate of absorption of the lowest layer 33.Similarly, the highest layer 35 and the lowest layer 33 may have ratesof absorption that are approximately equal to one another, such rate ofabsorption being greater or lesser than the rate of absorption of themiddle layer 33.

In addition, this embodiment of the matrix 32 is not limited to layers.The matrix 32 may be constructed in any configuration having materialsof different absorption rates in any portion of the matrix 32 that isdesired to promote wound healing. For example, as illustrated in FIG. 2b, the material on the periphery 36 of the matrix 32 may be constructedof material having one rate of absorption, while the inner portions 37of the matrix 32 may be constructed of one of more materials havingdifferent rates of absorption. This would allow for the wound 25 toclose at one rate during the initial portion of the treatment period,and for the wound 25 to close at different rates during later portionsof the treatment period. Other configurations that are possible includehaving approximately opposite sides or ends of the matrix 32 beingconstructed of a different material from the intermediate portions ofthe matrix 32.

The fluid-impermeable wound cover 40 in the embodiment of the reducedpressure appliance 30 illustrated in FIG. 1 is in the form of aflexible, adhesive, fluid impermeable polymer sheet for covering andenclosing the wound 25, including the absorbable matrix 32 within it,and the surrounding normal skin 24 at the wound site 25. The wound cover40 includes an adhesive backing 41 which functions to seal the woundcover 40 to the normal skin 24 around the periphery of the wound 25 toprovide a generally gas-tight or fluid-tight enclosure over the wound25. The adhesive cover sheet 40 must have sufficient adhesion to form afluid-tight or gas-tight seal 42 around the periphery of the wound 25and to hold the sheet 40 in sealed contact with the skin 24 during theapplication of suction or reduced or negative pressure. The wound cover40 also provides a gas-tight seal around the tubing 45 at thefeedthrough location 46 where the tubing 45 emerges from beneath thewound cover 40. The wound cover 40 is preferably formed of a fluidimpermeable or gas impermeable flexible adhesive sheet such as Ioban, aproduct of the 3M Corporation of Minneapolis, Minn.

The reduced pressure appliance 30 is not, however, limited to theconfiguration illustrated in FIG. 1. The appliance 30 may also have awound cover of almost any size, shape, and configuration adapted totreat the wound. An example of this type of cover 40 is illustrated inthe embodiment of the appliance 30 shown in FIG. 3, which has a woundcover 140 comprised of a rigid, fluid impermeable, generally cone-shapedwound cover 140 overlying the wound site 25. Alternatively, the coveroverlying the wound site may be comprised of a rigid, fluid impermeable,flat, bowl-shaped, or cup-shaped wound cover to protect the site of awound 25 from impact or abrasion during treatment. The wound cover mayalso be comprised of a fluid impermeable, flexible cover supported byrigid support members overlying the wound site 25. All of these covertypes may be sealed to the normal skin 24 surrounding the wound 25 byusing the suction created under the cover and a soft and flexiblepadding material 143 around the periphery of the cover 140, which is incontact with the skin 24. More preferably, the cover 140 is sealed tothe skin 24 using a fluid-impermeable adhesive material 141 such as anadhesive tape or an adhesive sheet that has been cut to surround and atleast partially overlie the periphery of the cover 140. As an additionalexample, the cover may be comprised of a CPR mask, which may be sealedto the skin surrounding the wound with an inflatable air cuff that is apart of the mask, with a fluid-impermeable adhesive material, or by someother fluid-impermeable means. Where the cover 140 is not in contactwith the absorbable matrix 32, and is therefore not exerting forceadequate to keep the matrix 32 in place within the wound 25, a rigid orsemi-rigid porous screen 147 may be placed over the matrix 32 and underthe cover 140 in a position so that the periphery of such screen 147 isheld in place by a portion of the cover 140 or the seal 142 that holdsthe cover 140 in place against the skin 24. In such case, the screen 147is of a thickness and rigidity necessary to hold the matrix 32 in placewithin the wound 25, but having a porous structure so that fluids(including gases) are able to pass through the screen 147.

The appliance 30 also includes a suction port in the form of a hollowsuction tube 45 that connects with the vacuum system 50 to providesuction within the sealed enclosure. The suction tubing 45 serves as asuction port for the appliance 30. In the embodiment of the inventionillustrated in FIG. 1, an end segment 45 a of the tubing 45 is embeddedwithin the absorbable matrix 32 for providing suction or reducedpressure within the enclosure provided under the wound cover 40.Embedding the open end of segment 45 a of tubing 45 within the interiorof the absorbable matrix 32 permits the absorbable matrix 32 to functionas a shield to help prevent the wound cover 40 from being inadvertentlysucked into sealing engagement with the open end of the tube therebyplugging the tube 45 and restricting gas flow. The tube segment 45 aembedded within the absorbable matrix 32 preferably has at least oneside port 47 for positioning within the interior of the absorbablematrix 32 to promote substantially uniform application of reducedpressure throughout the enclosure. Positioning the side port 47 of tubesegment 45 a within the interior of the absorbable matrix 32 permits theabsorbable matrix 32 to function as a shield for the side port tothereby prevent the wound cover 40 from being sucked into the side port47 and thereby restricting gas flow. The open cells of the absorbablematrix 32 facilitate gas flow throughout the enclosure. In addition, theabsorbable matrix 32 functions to encourage the growth of tissue in thearea of the wound 25 into the matrix 32 and to hold the wound cover 40generally out of contact with the wound 25 during the application ofsuction within the enclosure.

Tubing 45 and tube segment 45 a are sufficiently flexible to permitmovement of the tubing but are sufficiently rigid to resist constrictionwhen reduced pressure is supplied to the appliance 30 or when thelocation of the wound 25 is such that the patient must sit or lie uponthe tubing 45 or upon the reduced pressure appliance 30. The matrix-tubeassembly comprising the absorbable matrix 32 and the tube 45 may befabricated by snaking the end of the tube segment 45 a through aninternal passageway in the absorbable matrix 32 such as by pulling theend of the tube segment 45 a through the passageway using forceps. Thematrix-tube assembly 32 and 45 is preferably prepared prior to use understerile conditions and then stored in an aseptic package.

As shown in FIG. 4 a, the vacuum system 50, which produces a source ofreduced pressure or suction that is supplied to the reduced pressureappliance 30, includes a vacuum pump 51, a control device 52, a filter53, and tubing 54 that connects the vacuum pump 51 to the collectionsystem 70. Predetermined amounts of suction or reduced pressure areproduced by the vacuum pump 51. The vacuum pump 51 is preferablycontrolled by a control device 52 such as a switch or a timer that maybe set to provide cyclic on/off operation of the vacuum pump 51according to user-selected intervals. Alternatively, the vacuum pump 51may be operated continuously without the use of a cyclical timer. Afilter 53 such as micropore filter is preferably attached to the exhaustof the pump 51 to prevent potentially pathogenic microbes or aerosolsfrom being vented to atmosphere by the vacuum pump 51.

As shown in FIG. 4 a, a fluid collection system, generally designated70, is interconnected between the suction pump 51 and the appliance 30to remove and collect any exudate which may be aspirated from the wound25 by the reduced pressure appliance 30. The appliance 30 functions toactively draw fluid or exudate from the wound 25. Collection of exudatein a fluid collection system 70 intermediate the pump 51 and theappliance 30 is desirable to prevent clogging of the pump 51. The fluidcollection system 70 is comprised of a fluid-impermeable collectioncontainer 71 and a shutoff mechanism 75. The container 71 may be of anysize and shape capable of intercepting and retaining a predeterminedamount of exudate. Many examples of such containers are available in therelevant art. The preferred container in this embodiment of theinvention is illustrated in side elevation view in FIG. 4 a, saidcontainer having two openings in the top of the container 71. Thecontainer 71 includes a first port 72 at the top opening of thecontainer for sealed connection to suction tubing 45. The first port 72enables suction to be applied to the reduced pressure appliance 30through the tubing 45 and also enables exudate from the wound 25 coveredby reduced pressure appliance 30 to be drained into the container 71.The container 71 provides a means for containing and temporarily storingthe collected exudate. A second port 73 is also provided on the top ofthe container to enable the application of suction from the vacuum pump51. The second port 73 of the collection system 70 is connected to thevacuum pump 51 by a vacuum line 54. The collection system 70 is sealedgenerally gas-tight to enable the suction pump 51 to supply suction tothe appliance 30 through the collection system 70.

The container 71 may also include a fluid impenetrable flexible linerwithin its volume that is used to collect the exudate in a manner thatavoids contaminating the container 71 with pathogenic microbes and otherharmful matter present in the exudate. In such case, the flexible linermay be directly connected to the first port 72 and second port 73 in amanner so that no exudate comes into direct contact with the container71. In this embodiment, the preferred liner is a flexible bagconstructed of a polymer material, which is connected to the first port72.

The vacuum system 50 and collection system 70 preferably include ashutoff mechanism for halting or inhibiting the supply of the reducedpressure to the appliance 30 in the event that the exudate aspiratedfrom the wound 25 exceeds a predetermined quantity. Interrupting theapplication of suction to the appliance 30 is desirable to preventexsanguination in the unlikely event a blood vessel ruptures under thewound cover 40 during treatment. If, for example, a blood vesselruptures in the vicinity of the wound 25, a shut-off mechanism would beuseful to prevent the vacuum system 50 from aspirating any significantquantity of blood from the patient.

The shutoff mechanism 75 may be comprised of any means that enables thevacuum system 50 to halt the supply of reduced pressure to the woundcover 40 at any time that the volume of exudate from the wound 25exceeds a predetermined amount. Such means may include mechanicalswitches, electrical switches operably connected to the vacuum systemcontroller 52, optical, thermal or weight sensors operably connected tothe vacuum system controller 52, and any other means that are currentlyknown in the relevant art or which may hereafter be discovered. Theshutoff mechanism 75, as illustrated in FIG. 4 b, is preferably a floatvalve assembly in the form of a ball 76 which is held and suspendedwithin a cage 77 positioned below a valve seat 78 disposed within theopening at the top of the container below the second port that willfloat upon the exudate and will be lifted against the valve seat 78 asthe container fills with exudate. When the ball 76 is firmly seatedagainst the valve seat 78, the float valve blocks the second port 73 andthereby shuts off the source of suction from the vacuum system 50. Othertypes of mechanisms may also be employed to detect the liquid levelwithin the container 71 in order to arrest operation of the vacuumsystem 50.

In another version of the invention, the wound treatment apparatusincludes means to monitor the pressure beneath the wound cover 40 at thesite of the wound 25. In one embodiment of this version of theinvention, as illustrated in FIG. 5 a, the wound cover 40 has aplurality of protrusions 60 in the form of hills or bumps embedded inthe cover 40. As illustrated in FIG. 5 a, the protrusions 60 protrudeabove the remaining surface 43 of the cover 40 when the cover 40 is notin use for wound treatment. A detailed view of a protrusion 60 a in thisconfiguration is shown in perspective view in FIG. 5 b. Generally, asillustrated in FIG. 5 c, in some embodiments, when the cover 40 is inuse (i.e., sealed over the wound site 25 with reduced pressure appliedbeneath the cover 40), the protrusions 60 are displaced inwardly (ordownward when the cover 40 is in the orientation depicted in FIG. 5 c)so that they are depressed to a level almost the same as that of theremaining surface 43 of the cover 40. A detailed view of a protrusion 60b in the depressed configuration is shown in perspective view in FIG. 5d. In another embodiment, the protrusions 60 c are configured in theform of bellows, as shown in FIG. 5 e. In this version of the invention,as the pressure beneath the cover 40 decreases (i.e., the level ofreduced pressure increases), the top of the protrusion 60 c is displaceddownward toward the level of the remaining surface 43 of the cover 40.The protrusions 60 may be placed in any location, as well as in anypattern or lack of pattern, on the surface of the cover 40. An exampleof one possible pattern is illustrated in FIG. 5 f.

The protrusions 60 may be constructed of the same material as theremainder of the cover 40, or may be constructed of a material differentfrom the remainder of the cover 40, depending upon the sensitivity ofpressure monitoring desired. Similarly, the protrusions 60 may beconstructed of material having the same thickness as the remainder ofthe cover 40, or material of a different thickness, depending upon thesensitivity of pressure monitoring desired. For example, if the reducedpressure beneath the cover 40 is of a relatively low level, so that thedifference between the ambient atmospheric pressure above the cover 40is relatively small when compared to the reduced pressure beneath thecover 40, it may be desirable to have the protrusions 60 be able tochange shape with relatively small changes in pressure beneath the cover40 during the treatment period. In such case, it may be preferable tohave the protrusions 60 of a thickness less than the thickness of theremaining cover material. It may also be preferable to have theprotrusions 60 constructed of a material more pliable than the materialof which the remainder of the cover 40 is constructed. Similarly, if thereduced pressure beneath the cover 40 is of a relatively high level, sothat the difference between the ambient atmospheric pressure above thecover 40 is relatively large when compared to the reduced pressurebeneath the cover 40, it may be desirable to have the protrusions 60 beable to change shape with relatively large changes in pressure beneaththe cover 40 during the treatment period. In such case, it may bepreferable to have the protrusions 60 of a thickness more similar to thethickness of the remaining cover material. It may also be preferable tohave the protrusions 60 constructed of a material that is more similarto the material of which the remainder of the cover 40 is constructed interms of pliability.

By preselecting the thickness and pliability of the material used toconstruct the protrusions 60, it may also be possible to monitor thepressure by partial deflections of the protrusions 60. For example, theprotrusions 60 may be displaced in an increasing amount above theremaining surface 43 of the cover 40 as the pressure beneath the cover40 increases (i.e., the level of reduced pressure decreases). Thisrelationship of displacement of the protrusions 60 to the increase inpressure beneath the cover 40 may be linear or based upon some otherfunction. Similarly, the protrusions 60 may be constructed so that theyonly begin to be displaced when a predetermined pressure differentialoccurs between the area under the cover 40 and the area above the cover40. It should be noted, however, that this version of the invention isintended as a means to provide an inexpensive and approximate visualindication of the occurrence of loss of reduced pressure beneath thecover and may not be a means to accurately measure the actual pressurebeneath the cover or the actual difference between the pressure abovethe cover and the reduced pressure beneath the cover.

As a result, the preferable thicknesses and materials to be used inconstructing the cover 40 and protrusions 60 in this version of theinvention are dependent upon a multitude of factors, including thedesired pressure beneath the cover 40. Preferably, the wound cover 40 isconstructed of polyurethane, having a thickness of only a few mils to⅛th inch, and having protrusions 60 constructed of the same material asthe remaining portion of the cover 40, said protrusions 60 having athickness only slightly less than the thickness of the cover 40 to arelatively small fraction of the thickness of the cover 40.

Further, the protrusions 60 may be constructed of material that is of adifferent color than the color of the remaining surface 43 of the cover40. Similarly, the protrusions 60 may be of a different shade of thesame color as the remaining surface 43 of the cover 40. As theprotrusions 60 are displaced away from the remaining surface 43 of thecover 40, the protrusions 60 may change color as a result of theexpansion of the material comprising the protrusions 60.

In another embodiment of this version of the invention, the protrusionswork in the manner opposite to that described above. In this embodiment,the cover has within it a plurality of areas that are displaced away(i.e., pulled down) from the remaining surface of the cover toward thewound when reduced pressure is applied beneath the cover. This downwarddisplacement is the result of the reduced pressure suction, which causestension that pulls the protrusions away from the remaining surface ofthe cover. As the pressure beneath the cover increases, the tension onthe protrusions weakens allowing the protrusions to recede back into thecover. The principles discussed above with respect to thickness,materials, color, and partial deflection monitoring of pressure apply tothis embodiment of the invention as well. It should be noted thatbellows-type protrusions are not used in this embodiment.

The protrusions 60 may also have a means whereby they produce an audiblesound as the protrusions 60 are being displaced away from the remainingsurface 43 of the cover 40. This sound may be produced by the“crinkling” or vibration of the material as it is displaced away fromthe remaining surface 43 of the cover 40.

It should be noted that the means to monitor the pressure beneath thecover described in this embodiment of the invention may be usedindependently of any other feature of this invention. In addition, themeans to monitor pressure beneath the cover is not limited to use intreatment of open wounds, decubitus ulcers, dehisced incisions, partialthickness burns, and various lesions to which flaps or grafts have beenattached. Instead, said pressure monitoring means may be used in anyapplication involving reduced pressure in the treatment of any portionof the body of a patient, such as cosmetic surgery, cosmetic healing,and prophylactic suctioning for cosmetic and psychological reasons. Inaddition, the cover may be of any configuration, including the coverconfigurations specifically discussed above. Further, it is notnecessary that any packing material or matrix be present in the area ofthe wound beneath the cover in this version of the invention. Nor is itnecessary that the features included in this version of the invention beincluded as a part of any other version or embodiment of this invention.

In another version of the invention, the wound treatment apparatusincludes means to monitor the temperature in the area of the wound 25.In one embodiment of this second version of the invention, asillustrated in FIG. 6, a layer of temperature sensitive material 80 isplaced adjacent to the lower surface 44 of the wound cover 40.Alternatively, the cover 40 and the layer 80 may be joined together toform a single integrated unit. In such case, the cover 40 and the layer80 may be joined in any manner that is fluid-impermeable and allows thecolor (or other property exhibiting the change of temperature) of thetemperature sensitive layer 80 to be observed from above the wound cover40. The preferred means to join the cover 40 and the layer 80 is atransparent or semi-transparent adhesive material. Alternatively, thewound cover 40 may itself be composed of a temperature sensitivematerial, so that a separate temperature sensitive layer is notrequired.

The temperature sensitive layer 80 (or the cover 40, if it is composedof a temperature sensitive material) may be composed of any materialthat changes properties in a manner that does not adversely affect theoperation of the reduced pressure appliance 30. Preferably, thetemperature sensitive layer 80 is composed of a material that changescolor, or changes from one shade of a color to another shade of the samecolor, as the temperature of the material changes. The change in coloror shade preferably occurs within the temperature range that may beexpected in the area of the wound 25. In other words, the change incolor or shade of the material should be significant enough toadequately indicate changes in temperature within the range oftemperatures expected in the area of the wound 25. More preferably, thetemperature sensitive material is a material that changes color in therange from approximately 95 degrees Fahrenheit to approximately 105degrees Fahrenheit.

In the embodiment of the invention shown in FIG. 6, the temperaturesensitive layer 80 is placed over a packing material or matrix 32 a,which packing material or matrix 32 a is placed within the area of thewound 25. The matrix 32 a may be an absorbable matrix 32 a, as describedabove. The packing material may be constructed of any material that issuitable for placement within a wound 25, which may be to prevent itsovergrowth, but still allows for fluid and gas flow to and from thewound 25, such as a porous polymer material or gauze. In order toprovide for uniform temperature monitoring, the packing material ormatrix 32 a is preferably of relatively uniform thickness when placedwithin the area of the wound 25. In addition, the packing material ormatrix 32 a should be thin enough to allow for the temperature of thetissue to affect the temperature of the temperature sensitive layer 80.More preferably, the thickness of the packing material or matrix 32 ashould not exceed slightly greater than zero to one half inches. Thepacking material or matrix 32 a may, however, be of non-uniformthickness where the temperature sensitive layer 80 is comprised oftemperature sensitive material in a manner that compensates for thedifferences in thickness of the packing material or matrix 32 a.

The wound cover 40 is placed over the temperature sensitive layer 80 andsealed to the normal skin 24 surrounding the wound 25. If the cover 40and the temperature sensitive layer 80 are an integrated unit, however,the unit is placed over the packing material or matrix 32 a without aseparate temperature sensitive layer 80. If the cover 40 is composed ofa temperature sensitive material, it is placed over the packing materialor matrix without an additional temperature sensitive layer 80. Itshould be noted, however, that the temperature sensitive material usedin this embodiment of the invention is intended as a means to provide anapproximate visual indication of the temperature in the area of thewound 25 beneath the cover 4, and may not accurately measure the actualtemperature beneath the cover 40.

In another embodiment of this second version of the invention, one ormore temperature measuring devices 81 are placed within the area of thewound 25 and connected to an alarm system, generally designated as 82.The temperature measuring devices 81 may also be connected to atemperature display and recording device 83. An example of thisembodiment is illustrated in FIG. 7, which shows temperature measuringdevices 81 placed in the area of the wound 25. The temperature measuringdevices 81 may be placed in any area of the wound 25 and the reducedpressure appliance 30. For example, the temperature measuring devices 81may be placed adjacent to and in direct contact with the tissue in thearea of the wound 25. Alternatively, the temperature measuring devices81 may be embedded in any packing material or matrix 32 placed in thearea of the wound 25, or in the area between such packing material ormatrix 32 and the cover 40, or embedded within the cover 40, or adjacentto either surface of the cover 40.

The temperature measuring devices 81 are preferably capable of measuringtemperatures in the range of temperatures expected in the area of thewound 25. More preferably, the temperature measuring devices 81 arecapable of measuring temperatures in the range of 95 degrees Fahrenheitto 105 degrees Fahrenheit. The temperature measuring devices 81 may beany device that measures temperature in the desired range and produces acorresponding signal that may be interpreted by the alarm system 82 andtemperature display and recording device 83. The temperature measuringdevices 81 must, however, not be harmful to body tissue. The temperaturemeasuring devices 81 are preferably thermocouples or optical sensors ordetectors. The temperature measuring devices 81 are more preferablythermocouples that generate an electronic signal representing thetemperature measured by the thermocouple.

The temperature measuring devices 81 are connected by leads 84 to analarm system 82. The leads 84 may be in any form compatible with thetemperature measuring devices 81 and the alarm system 82 and recordingdevice 83. Preferably, the leads 84 are cables or wires constructed ofan electrically conductive material, optical fiber, or other mediumenabling data transmission that transfers the signals from thetemperature measuring devices 81 to the alarm system 82 and the displayand recording device 83. Leads 84 placed under the wound cover 40feedthrough the seal 42 beneath the cover 40 in a manner similar to thatfor the tubing (as illustrated and discussed above in connection withFIG. 1) that maintains the fluid impermeable nature of the seal 42.

The alarm system 82 is comprised of a computer or other data processor85 and an alarm device 86. The computer or data processor 85 receivesthe signals from the temperature measuring devices 81 and converts themto electronic or other signals that are recognized by the alarm device86. The computer or data processor 85 is of a type that is commonlyavailable in the relevant art. The alarm device 86 may produce any typeof audible sound as an alarm, such as a ringing sound, buzzing, chirpingor other common alarm noise. Alternatively, the alarm device 86 mayinclude a digitally produced audible voice that presents predeterminedmessages corresponding to different temperature conditions in the areaof the wound 25. The alarm device 86 preferably produces differentlevels of alarm depending upon the temperature measurements receivedfrom the temperature measuring devices 81. For example, as thetemperature drops below or rises above successive preselected values oftemperature, as measured by any temperature measuring device 81, thealarm device 86 may sound successive predetermined alarm pitches,sounds, messages or series of sounds. Similarly, as the temperaturemeasured by multiple temperature measuring devices 81 successively fallsbelow or rises above a preselected temperature, the alarm device 86 maysound successive predetermined alarm pitches, sounds, messages or seriesof sounds. The alarm system 82 may also be connected to the vacuumsupply 50, so that upon production of a predetermined alarm by the alarmdevice 86, the vacuum pump controller 52 causes the pump 51 to ceaseoperation.

The computer or data processor 85 may also be connected to a temperaturedisplay and recording device 83 that records the temperatures measuredby one or more of the temperature measuring devices 81. The temperaturerecording device 83 may be any device designed to record or display datathat is compatible with the signals produced by the computer or dataprocessor 85. Such devices are preferably devices that record data oncompact disks, floppy disks, magnetic tape, integrated circuits, orother similar media in digital form or “manual” devices that record ordisplay data in a visually depicted form, such as a chart recorder orvisual electronic display, such as an LCD or CRT monitor. The morepreferred temperature display and recording device 83 is a devicerecording data on a compact disk used in conjunction with an LCDmonitor.

It should be noted that in this embodiment of this version of theinvention the cover 40 may be of any configuration, including the coverconfiguration illustrated in FIG. 3 and the other cover configurationsspecifically discussed above in connection with FIG. 3. In addition, itis not necessary that any packing material or matrix 32 be present inthe area of the wound 25 beneath the cover 40 in this version of theinvention. It is also not necessary that the temperature display andrecording device 83 be included in every embodiment of this version ofthe invention. Nor is it necessary that the features included in thisversion of the invention be included as a part of any other version orembodiment of this invention.

In another version of the invention, the wound treatment apparatus 220is portable and may be self-contained. In a first embodiment of thisversion of the invention, as illustrated in FIG. 8 a, a miniature andportable vacuum source 250 is connected to a wound cover. The vacuumsource 250 is preferably a miniature and portable vacuum pump. Thevacuum source 250 may also be connected to a filter 253, which isconnected to a collection system 270. The vacuum source 250 is used toprovide suction to the reduced pressure appliance, generally designatedas 230. It is portable in the sense that it is of a size small enough tobe positioned directly on the surface of the wound cover 240. The vacuumsource 250 is also lightweight to avoid placing too much pressure on anybody part being treated by the apparatus 220 and to allow the apparatus220 to be easily transported. The vacuum source 250 may be powered byelectricity received through a cord plugged into a standard wall socket,or the vacuum source 250 may be powered by a battery, fuel cell, orother alternative means, such as solar or photo electric sells or awindmill or watermill operated generator. The vacuum source 250 may alsobe operated by other means, such as pneumatics or hydraulics, if suchmeans are available.

The wound cover 240 may be of almost any size, shape, and configurationadapted to treat the wound. Thus, the wound cover 240 is not limited tothe embodiment illustrated in FIG. 8 a. As illustrated and discussedabove in relation to FIG. 3, the cover may be comprised of a rigid,fluid impermeable, cone-shaped, bowl-shaped, or cup-shaped wound coverto protect the site of a wound 25 from impact or abrasion duringtreatment. Alternatively, the cover may be comprised of a flexible orrigid flat wound cover.

The vacuum source 250 may be attached to the cover 240 using any meansthat is compatible with the structure of the cover 240 and the vacuumsource 250. For example, if the cover 240 is constructed of a flexible,fluid impermeable material, the vacuum source 250 may be attached to thecover 240 using an adhesive material, such as a glue or other liquid orsprayed adhesive, adhesive tape, and similar means that are currentlyknown in the relevant art or which may hereafter be discovered. Asanother example, if the wound cover 240 is constructed of a rigidmaterial, the vacuum source 250 may be attached to the cover 240 using avariety of fasteners and similar means, such as anchors, bolts, rivets,screws, nuts, latch and clasp, hook and loop fasteners (such as thatcommonly sold under the trade name VELCRO), ultrasonic welding, andsimilar structures that are currently known in the relevant art or whichmay hereafter be discovered. The vacuum source 250 may therefore bepermanently attached to the cover 240, or the vacuum source 250 may beremovably attached to the cover 240 allowing the vacuum source 250 to bereused after being used for a treatment even if the cover 240 is nolonger usable after such treatment. The means of fastening the vacuumsource 250 to the cover 240 must, however, be accomplished in a mannerthat allows the cover 240 to maintain the desired reduced pressurebeneath the cover 240 while it is in use. Thus, gasket or sealantmaterial may be used to seal any areas of perforation of the cover 240where the fastener penetrates the surface of the cover 240.

The fluid collection system 270 in the embodiment illustrated in FIG. 8a includes a container 271 to collect the exudate and a shutoffmechanism 275, one embodiment of which is illustrated in FIG. 8 b, tohalt operation of the vacuum source 250 if the level of exudate in thecontainer 271 exceeds a predetermined level. The container 271 is of theminimum size desired to collect and maintain the amount of exudateexpected to be aspirated from the wound during the time of anticipateduse of the portable wound treatment apparatus 220. Alternatively, asmall container 271 may be used, in which the fluid is changedintermittently as necessary during the treatment period. The container271 has two ports, a first port 272 for connecting the container 271 tothe reduced pressure appliance 230 and a second port 273 for connectingthe container 271 to the vacuum source 250. A filter 253 may also beconnected intermediate the vacuum source 250 and the container 271. Theshutoff mechanism may be comprised of any means that enables the vacuumsystem 250 to halt the supply of reduced pressure to the wound cover 240at any time the volume of exudate from the wound exceeds a predeterminedamount to prevent, thereby preventing such exudate from contaminatingthe vacuum source 250. Such means may include mechanical switches,electrical switches operably connected to the vacuum source 250,optical, thermal or weight sensors operably connected to the vacuumsource 250, and any other means that are currently known in the relevantart or which may hereafter be discovered. Where the shutoff mechanismtransfers electrical or other data signals to the vacuum source 250, thevacuum source 250 may contain a control mechanism to convert saidsignals to the form necessary to halt the production of reduced pressureby the vacuum source 250. Such means is preferably the float valveshutoff mechanism 275 illustrated in FIG. 8 b, connected to the secondport 273 of the container 271, which has the same features as the floatvalve illustrated in and discussed above in connection with FIG. 4 a.

As illustrated in FIG. 8 a, this embodiment of the invention may alsoinclude a filter 253 to prevent potentially pathogenic microbes oraerosols from contaminating the vacuum source 250. The filter 253 isgenerally comprised of a filter element encased in a fluid impermeablehousing that has an inlet port 256 and an outlet port 257. The filterelement is preferably a hydrophobic and micropore filter capable offiltering out pathogenic microbes or aerosols. The housing of the filter253 may be constructed in a manner that enables the filter element to bechanged if desired. The filter 253 need not, however, be used in everyembodiment of this version of the invention.

In the embodiment illustrated in FIG. 8 a, tubing 245 is used to connectthe reduced pressure appliance 230 covering a wound 225 to thecollection system 270 by means of the first port 272 located on thecontainer 271. The features of this tubing 245 and reduced pressureappliance 230 are substantially the same as illustrated and discussedabove in connection with FIG. 1 and FIG. 4 a. In addition, in theembodiment of the invention illustrated in FIG. 8 a, the second port 273of the container 271 is connected to the inlet port 256 of the filter253 by flexible vacuum tubing 254, such as that used to connect thecollection system 270 to the reduced pressure appliance 230. This isnot, however, the only means of connecting the collection system 270 tothe filter 253. For example, the connection may be made by using arigid, fluid impermeable structure, such as a short length of rigidpolymer tube, permanently connecting the filter 253 and the collectionsystem 270. The filter 253 may also be directly attached to thecontainer 271 without the use of any tubing or other means, causing thecontainer 271 and the filter 253 to be integrated as a single unit. Inthe embodiment of the invention illustrated in FIG. 8 a, the outlet port257 of the filter 253 is connected to the vacuum source 250 by flexiblevacuum tubing 254 a, such as that used to connect the collection system270 to the reduced pressure appliance 230. This is not, however, theonly means of connecting the collection system 270 to the filter 253.For example, the connection may be made by using a rigid, fluidimpermeable structure, such as a short length of rigid polymer tubepermanently connecting the filter 253 and the vacuum source 250. Thefilter 253 may also be directly attached to the vacuum source 250without the use of any tubing or other means, causing the container 271and the filter 253 to be integrated as a single unit. As illustrated inFIG. 8 a, the vacuum source 250, the filter 253, and the container 271may also be directly attached to one another to form a single integratedunit. Such attachment may be made by any of the means described abovethat may be used to attach the vacuum source 250 to the cover 240.

Use of the wound treatment apparatus can be illustrated by a prospectiveexample involving a reduced pressure appliance 30 of the type discussedin connection with FIG. 1. After preparing the bed of the wound 25, oneend of a length of vacuum tubing 45 is embedded in an absorbable matrix32 that is trimmed to be the size and shape of the wound 25. The matrix32 is saturated with saline and placed in the wound 25. As illustratedin FIG. 7, if temperature monitoring is desired, temperature measuringdevices 81 are placed in the desired locations and connected to an alarmsystem 82, and if desired, a display and recording device 83.Alternatively, a temperature sensitive layer 80 is placed over thematrix, as illustrated in FIG. 6. A fluid impermeable or gas impermeableflexible adhesive sheet 40, such as IOBAN, is placed over the matrix 32(and temperature measuring means, if utilized) and the wound 25 andsealed to the normal skin 24 surrounding the wound 25. The site offeedthrough of the vacuum tube 45 and any leads 84 from under the cover40 is then sealed with a liquid or paste adhesive. Negative pressure isthen applied to the reduced pressure appliance 30 by the vacuum system50, through the intermediate fluid collection system 70.

Negative pressure appliances are useful for treating a variety ofwounds. Treatment of a wound can be carried out by securing a negativepressure appliance to the treatment site as previously shown anddescribed, and then maintaining a substantially continuous or cyclicalreduced pressure within the appliance until the wound has reached adesired improved condition. A selected state of improved condition mayinclude formation of granulation tissue sufficient for the attachment ofa flap or graft, reduction of microbial infection in the wound, arrestor reversal of burn penetration, closure of the wound, integration of aflap or graft with the underlying wounded tissue, complete healing ofthe wound, or other stages of improvement or healing appropriate to agiven type of wound or wound complex.

It may be preferable to change the appliance periodically duringtreatment, particularly when using appliances incorporating a packingmaterial on or in the wound. The time between changing the appliancewhere an absorbable matrix is placed on or in the wound would ordinarilybe a greater time interval that is generally dependent upon the natureof the wound. Where it is necessary to change the absorbable matrixduring the treatment period, it may also be necessary to remove aportion of the matrix, but leave in place the portion of the matrix intowhich there has been significant tissue growth. In such cases, theportion of the matrix without significant tissue growth incorporatedtherein should be carefully removed by cutting or tearing away suchportion from the remaining portion. New absorbable material can beplaced in the area from which the prior material has been removed.

The wound treatment apparatus is preferably operated using a negative orreduced pressure ranging from 0.01 to 0.99 atmospheres, and morepreferably practiced using a negative or reduced pressure rangingbetween 0.5 to 0.8 atmospheres. The time period for use of the woundtreatment apparatus on a wound may preferably be at least 12 hours, butcan be, for example, extended for one or more days. There is no upperlimit beyond which use of the wound treatment apparatus is no longerbeneficial; use of the wound treatment apparatus increases the rate ofclosure up to the time the wound actually closes. Satisfactory treatmentof various types of wounds has been obtained via the use of reducedpressures equivalent to about 2 to 7 in. Hg below atmospheric pressure.

Supplying reduced pressure to the appliance in an intermittent or cyclicmanner has also been demonstrated to be useful for treating wounds.Intermittent or cyclic supply of reduced pressure to an appliance may beachieved by manual or automatic control of the vacuum system 50. A cycleratio, the ratio of “on” time to “off” time, in such an intermittentreduced pressure treatment may be as low as 1:10 or as high as 10:1. Thepreferred ratio is approximately 1:1 which is usually accomplished inalternating 5 minute intervals of reduced pressure supply andnon-supply.

A suitable vacuum system 50 includes any suction pump capable ofproviding at least 0.1 pounds of suction to the wound, and preferably upto three pounds suction, and most preferably up to fourteen (14) poundssuction. The pump can be any ordinary suction pump suitable for medicalpurposes that is capable of providing the necessary suction. Thedimension of the tubing interconnecting the pump and the reducedpressure appliance is controlled by the pump's ability to provide thesuction level needed for operation. A ¼ inch diameter tube may besuitable.

In treating damaged tissue, use of the invention usually comprises thesteps of applying negative pressure to a wound for a selected time andat a selected magnitude sufficient to reduce bacterial density in thewound. Open wounds are almost always contaminated with harmful bacteria.The application of negative pressure to a wound appears to reduce thebacterial density of the wound. It is believed that this effect is dueto either the bacteria's incompatibility with a negative pressureenvironment or the increased blood flow to the wound area, as bloodbrings with it cells and enzymes to destroy the bacteria.

Burns may generally be treated using a method that comprises the stepsof applying negative pressure to the burn over an area withpredetermined reduced pressure and for a time sufficient to inhibitformation of a full thickness burn. A partial thickness burn, one whichhas a surface layer of dead tissue and an underlying zone of stasis, isoften sufficiently infected so that it will transform within 24-48 hoursinto a full thickness burn, one in which all epidermal structures aredestroyed. The application of negative pressure to the wound preventsthe infection from becoming sufficiently severe to cause destruction ofthe underlying epidermal structures. The magnitude, pattern, andduration of pressure application can vary with the individual wound.

1. A method of treating a wound, comprising: positioning a cover overthe wound, the cover being at least liquid impermeable; applying areduced pressure to a space between the cover and the wound; andmonitoring the reduced pressure in the space between the cover and thewound by visually observing a pressure monitoring element supported bythe cover; wherein: the pressure monitoring element comprises at leastone surface that is in communication with the space between the coverand the wound; and at least one surface of the pressure monitoringelement is configured to move relative to a portion of the coversurrounding the pressure monitoring element that is also exposed to thereduced pressure in response to a change in reduced pressure within thespace between the cover and the wound.
 2. The method of claim 1, whereinthe reduced pressure is from about 2 in. Hg below atmospheric pressureto about 7 in. Hg below atmospheric pressure.
 3. The method of claim 1,wherein the reduced pressure is applied in a cyclic nature.
 4. Themethod of claim 1, wherein applying a reduced pressure to a spacebetween the cover and the wound comprises supplying reduced pressurefrom a portable vacuum source that is supportable by the cover or spacedapart from the cover.
 5. The method of claim 1, further comprisingcollecting wound exudate in a container, wherein the container issupportable by the cover or spaced apart from the cover.
 6. The methodof claim 5, wherein collecting wound exudate in a container comprisesdrawing wound exudate through a length of tubing in communication withthe cover and the container.
 7. The method of claim 5, whereincollecting wound exudate in a container comprises drawing wound exudatethrough a length of tubing having one end in communication with acollection container and another end connected to a port supported bythe cover.
 8. The method of claim 1, wherein foam, porous polymermaterial, gauze, soft flexible padding, an absorbable matrix, or othermaterial is positioned between the wound and the cover.
 9. The method ofclaim 1, further comprising monitoring an alarm, the alarm being incommunication with the cover and being configured to alert a user when athreshold value is reached within the cover.
 10. The method of claim 1,comprising sealing or adhering the cover to at least tissue surroundingthe wound so as to create a generally fluid-tight or gas-tight sealbetween the cover and the tissue surrounding the wound.
 11. The methodof claim 1, further comprising positioning an adhesive strip over atleast a portion of the cover to seal the cover.
 12. The method of claim1, wherein the cover is formed from or comprises a sheet of flexiblepolymer material.
 13. The method of claim 1, wherein monitoring thereduced pressure in the space between the cover and the wound byvisually observing the pressure monitoring element supported by thecover comprises monitoring whether a predetermined level of reducedpressure has been achieved in the space between the cover and the wound.14. The method of claim 1, wherein the pressure monitoring elementproduces an audible sound when moving from a first position to a secondposition relative to the portion of the cover surrounding the pressuremonitoring element.
 15. The method of claim 1, wherein applying areduced pressure to a space between the cover and the wound comprisessupplying reduced pressure from a battery powered vacuum source.
 16. Themethod of claim 1, wherein monitoring the reduced pressure in the spacebetween the cover and the wound comprises determining whether at least athreshold level of reduced pressure has been achieved under the cover.17. The method of claim 1, wherein the pressure monitoring elementcomprises a pliable material.
 18. The method of claim 1, wherein the atleast one surface of the pressure monitoring element is a collapsiblewall.
 19. The method of claim 1, further comprising monitoring acondition under the cover using an electronic sensor.
 20. The method ofclaim 1, wherein positioning the cover over the wound comprisespositioning the cover over an incisional wound.
 21. The method of claim20, wherein the incisional wound is a dehisced incisional wound.
 22. Themethod of claim 1, wherein positioning the cover over the woundcomprises positioning the cover over an open wound.
 23. The method ofclaim 1, further comprising positioning a sealing ring around the woundto seal the cover to tissue surrounding the wound.
 24. A method oftreating a wound, comprising: positioning a cover over the wound, thecover being at least liquid impermeable; applying a reduced pressure toa space between the cover and the wound; and monitoring the reducedpressure in the space between the cover and the wound by visuallyobserving a pressure monitoring element supported by the cover; whereinmonitoring the reduced pressure in the space between the cover and thewound comprises monitoring a displacement of one or more protrusionssupported by or integrally formed on the cover.
 25. The method of claim24, wherein each of the one or more protrusions is configured todisplace toward the wound as the reduced pressure between the cover andthe wound increases such that the amount of inward displacement of theprotrusion increases as the reduced pressure between the cover and thewound increases.
 26. The method of claim 24, wherein at least oneprotrusion has the shape of a hill, a bump, or a bellows.
 27. The methodof claim 24, wherein at least a portion of the pressure monitoringelement has a color different from the color of the remaining surface ofthe cover, or a different shade of the same color as the shade of thecolor on the remaining surface of the cover, and wherein the color orthe shade of the color of the pressure monitoring element changes as thepressure monitoring element is displaced away from the remaining surfaceof the cover.
 28. The method of claim 24, wherein monitoring adisplacement of one or more protrusions supported by or integrallyformed on the cover comprises monitoring a displacement or collapse ofat least one wall portion of one or more protrusions supported by orintegrally formed on the cover.
 29. The method of claim 24, wherein atleast one of the one or more protrusions comprises a curved surface. 30.The method of claim 24, wherein at least one of the one or moreprotrusions comprises a closed end portion and an open end portion. 31.The method of claim 24, wherein the one or more protrusions areconfigured to collapse toward the cover so as to be approximately levelwith the cover.
 32. The method of claim 24, wherein the one or moreprotrusions are made from a material that is different from that of thecover.
 33. The method of claim 24, wherein positioning the cover overthe wound comprises positioning the cover over an incisional wound. 34.The method of claim 33, wherein the incisional wound is a dehiscedincisional wound.
 35. The method of claim 24, wherein positioning thecover over the wound comprises positioning the cover over an open wound.36. A method of treating a wound, comprising: positioning a cover overthe wound, the cover being at least liquid impermeable; applying areduced pressure to a space between the cover and the wound; andmonitoring the reduced pressure in the space between the cover and thewound by visually observing a pressure monitoring element supported bythe cover; wherein monitoring the reduced pressure in the space betweenthe cover and the wound comprises monitoring one or more protrusionssupported by the cover, each protrusion being configured to move betweenat least an expanded state and a compressed state, and wherein each ofthe one or more protrusions is configured to move toward the compressedstate as the level of reduced pressure between the cover and the woundincreases.
 37. The method of claim 36, wherein the one or moreprotrusions are configured to move from an expanded state to acompressed state when a predetermined level of reduced pressure has beenachieved in the space between the cover and the wound.
 38. The method ofclaim 36, wherein applying a reduced pressure to a space between thecover and the wound comprises supplying reduced pressure from a portablevacuum source that is supportable by the cover or spaced apart from thecover.
 39. The method of claim 36, further comprising collecting woundexudate in a container, wherein the container is supportable by thecover or spaced apart from the cover.
 40. The method of claim 39,wherein collecting wound exudate in a container comprises drawing woundexudate through a length of tubing in communication with the cover andthe container.
 41. The method of claim 39, wherein collecting woundexudate in a container comprises drawing wound exudate through a lengthof tubing having one end in communication with a collection containerand another end connected to a port supported by the cover.
 42. Themethod of claim 36, wherein foam, porous polymer material, gauze, softflexible padding, an absorbable matrix, or other material is positionedbetween the wound and the cover.
 43. The method of claim 36, furthercomprising sealing or adhering the cover to at least tissue surroundingthe wound so as to create a generally fluid-tight or gas-tight sealbetween the cover and the tissue surrounding the wound.
 44. The methodof claim 36, wherein the cover is formed from or comprises a sheet offlexible polymer material.
 45. The method of claim 36, furthercomprising positioning a sealing ring around the wound to seal the coverto tissue surrounding the wound.
 46. A method of treating a wound,comprising: positioning a cover over the wound, the cover being at leastliquid impermeable; applying a reduced pressure to a space between thecover and the wound through a conduit, the conduit being incommunication with the cover and a vacuum source; and monitoring theexistence of or an amount of reduced pressure in the space between thecover and the wound by visually observing a pressure monitor comprisinga protrusion protruding away from a surface of the cover, the protrusionconfigured to displace downwardly in response to a level of reducedpressure between the cover and the wound.
 47. The method of claim 46,wherein the conduit is connected to a port supported by the cover. 48.The method of claim 46, comprising sealing or adhering at least aperiphery of the cover to tissue surrounding the wound.
 49. The methodof claim 46, further comprising positioning foam, porous polymermaterial, gauze, soft flexible padding, an absorbable matrix, or otherpacking material beneath the cover.
 50. The method of claim 46, whereinthe reduced pressure is applied in a cyclic nature.
 51. The method ofclaim 46, wherein applying a reduced pressure to a space between thecover and the wound comprises supplying reduced pressure from a portablevacuum source that is supportable by the cover or spaced apart from thecover.
 52. The method of claim 46, further comprising collecting woundexudate in a container, wherein the container is supportable by thecover or spaced apart from the cover.
 53. The method of claim 52,wherein collecting wound exudate in a container comprises drawing woundexudate through a length of tubing in communication with the cover andthe collection container.
 54. The method of claim 46, further comprisingmonitoring an alarm, the alarm being in communication with the cover andbeing configured to alert a user when a threshold value is reachedwithin the cover.
 55. The method of claim 46, further comprisingpositioning an adhesive strip over at least a portion of the cover toseal the cover.
 56. The method of claim 46, wherein the protrusion hasthe shape of a hill, a bump, or a bellows.
 57. The method of claim 46,wherein the cover is formed from or comprises a sheet of flexiblepolymer material.
 58. The method of claim 46, further comprisingproducing an audible sound associated with movement of the pressuremonitor from a first position to a second position.
 59. The method ofclaim 46, wherein applying a reduced pressure to a space between thecover and the wound comprises supplying reduced pressure from a batterypowered vacuum source.
 60. The method of claim 46, wherein monitoringthe existence of or an amount of reduced pressure in the space betweenthe cover and the wound comprises determining whether at least athreshold level of reduced pressure has been achieved under the cover.61. The method of claim 46, wherein the pressure monitor comprises apliable material.
 62. The method of claim 46, wherein the pressuremonitor comprises a collapsible wall.
 63. The method of claim 46,wherein the pressure monitor comprises at least one curved surface. 64.The method of claim 46, further comprising positioning a soft, flexiblepadding material in contact with the skin under the cover.
 65. Themethod of claim 46, further comprising monitoring a condition under thecover using an electronic sensor.
 66. The method of claim 46, whereinapplying a reduced pressure to a space between the cover and the woundcomprises supplying reduced pressure from a battery powered vacuumsource.
 67. The method of claim 46, wherein positioning the cover overthe wound comprises positioning the cover over an incisional wound. 68.The method of claim 67, wherein the incisional wound is a dehiscedincisional wound.
 69. The method of claim 46, wherein positioning thecover over the wound comprises positioning the cover over an open wound.70. A method of treating a wound, comprising: positioning an occlusiveor semi-occlusive dressing over the wound, the dressing comprising oneor more expandable areas that expand relative to the surroundingportions of the dressing in the presence of atmospheric pressure; andapplying sub-atmospheric pressure to the dressing; wherein the one ormore expandable areas contract toward the dressing relative to thesurrounding portions of the dressing that are also exposed to thesub-atmospheric pressure when the dressing is under sub-atmosphericpressure.
 71. The method of claim 70, wherein the one or more expandableareas contract toward the dressing at a sub-atmospheric pressure of 5mmHg to 50 mmHg.
 72. The method of claim 70, wherein the one or moreexpandable areas comprise one or more mountains having a pyramidal,cylindrical, square or other three-dimensional shape.
 73. The method ofclaim 70, comprising applying the sub-atmospheric pressure with asuction pump.
 74. The method of claim 73, wherein the sub-atmosphericpressure is applied via tubing.
 75. The method of claim 74, wherein thesub-atmospheric pressure is in communication with a canister.
 76. Themethod of claim 73, further comprising distributing the sub-atmosphericpressure across the wound through a matrix material of gauze or foam.77. The method of claim 75, wherein the sub-atmospheric pressure isfurther in communication with an overflow/bacterial filter.
 78. A methodof treating a wound, comprising: positioning a wound dressing apparatusover the wound, comprising positioning an at least liquid impermeablecover over the wound so as to create a substantially sealed spacebetween the cover and the wound; applying reduced pressure to the spacebetween the cover and the wound; and monitoring the reduced pressure inthe space between the cover and the wound by visually observing apressure indicator device supported by the wound dressing apparatus, thepressure indicator device comprising at least one surface that isconfigured to move relative to a portion of the wound dressing apparatussurrounding the pressure indicator device that is also exposed to thereduced pressure in response to a change in reduced pressure within thespace.
 79. The method of claim 78, wherein the at least one surface isconfigured to move toward the wound when the level of reduced pressurein the space increases to a greater reduced pressure value, and to moveaway from the wound when the level of reduced pressure in the spacedecreases.
 80. The method of claim 78, wherein applying a reducedpressure to a space between the cover and the wound comprises supplyingreduced pressure from a portable vacuum source that is supportable bythe cover or spaced apart from the cover.
 81. The method of claim 78,further comprising collecting wound exudate in a container, wherein thecontainer is supportable by the cover or spaced apart from the cover.82. The method of claim 81, wherein collecting wound exudate in acontainer comprises drawing wound exudate through a length of tubinghaving one end in communication with a collection container and anotherend connected to a port supported by the cover.
 83. The method of claim78, wherein foam, porous polymer material, gauze, an absorbable matrix,soft flexible padding, or other material is positioned between the woundand the cover.
 84. The method of claim 78, further comprising monitoringan alarm, the alarm being in communication with the cover and beingconfigured to alert a user when a threshold value is reached within thecover.
 85. The method of claim 78, further comprising sealing oradhering the cover to at least the tissue surrounding the wound so as tocreate a generally fluid-tight or gas-tight seal between the cover andthe tissue surrounding the wound.
 86. The method of claim 78, furthercomprising positioning an adhesive strip over at least a portion of thecover to seal the cover.
 87. The method of claim 78, further comprisingproducing an audible sound associated with movement of the pressuremonitoring element from a first position to a second position.
 88. Themethod of claim 78, wherein applying a reduced pressure to a spacebetween the cover and the wound comprises supplying reduced pressurefrom a battery powered vacuum source.
 89. The method of claim 78,wherein monitoring the reduced pressure in the space between the coverand the wound comprises determining whether at least a threshold levelof reduced pressure has been achieved under the cover.
 90. The method ofclaim 78, wherein the pressure monitoring element comprises a pliablematerial.
 91. The method of claim 78, wherein the at least one surfaceof the pressure monitoring element is a collapsible wall.
 92. The methodof claim 78, further comprising monitoring a condition under the coverusing an electronic sensor.
 93. The method of claim 78, whereinpositioning the wound dressing apparatus over the wound comprisespositioning the wound dressing apparatus over an incisional wound. 94.The method of claim 93, wherein the incisional wound is a dehiscedincisional wound.
 95. The method of claim 78, wherein positioning thewound dressing apparatus over the wound comprises positioning the wounddressing apparatus over an open wound.
 96. The method of claim 78,further comprising positioning a sealing ring around the wound to sealthe cover to tissue surrounding the wound.